TMJ, like others say, it depends on the child whether or not you might need to advocate. You mention that the psych wants to retest before school. If the results of that test indicate your child is MG+, then I would consider mentioning something to the school.
In my case, due to behavior issues with my DS in pre-K, DH and I had him tested privately and confirmed our suspicions that he was in fact gifted, and that many of his behavior issues in school were due to the fact that he wasn't challenged. So in our case, it was a necessity to bring up the issue with the school where he is currently attending kindergarten. In fact, I went to the school last May, and met with the principal, which started the process of the school doing their own reading and math assessments of my son. They worked on a plan for my son which I reviewed with them (several teachers and administrators) before the start of school last week. After the meeting, one of the administrators was very appreciative of the fact that I came to them as early as I did, because it gave them time to make accommodations for my son before the school year began.
Again, not sure if your son will need accommodations, but if he does, the school may appreciate the heads up.
